(1) Field of the Invention
The invention relates to bearing materials. More particularly, the invention relates to anti-friction materials for journal bearings.
(2) Description of the Related Art
Journal bearings are used as structural supports for rotating parts. Hydrodynamic bearings utilize a film of liquid lubricant between the journal pin and bushing. In common configurations, the journal pin is formed of a relatively rigid, non-lubricious, material. The bushing, or at least a surface layer thereof, is formed of a more compliant, more lubricious, bearing material. Advantageous properties for such bearing materials involve an appropriate combination of lubricity, high thermal conductivity, and fatigue strength. Lubricity is desirable even in the context of a hydrodynamic bearing to augment the liquid lubricant and address abnormal conditions causing local or total loss of liquid lubricant. Common metallic journal bearing materials include alloys or other combinations of tin, lead, aluminum, silver, and copper. Of particular interest are the journal bearings of planetary gears in fan drive gear systems for turbofan engines. Exemplary bearing material in that application utilizes copper as a base constituent and lead as a solid lubricant. Exemplary lead concentrations are 21-30% by weight. Exemplary manufacturing techniques involve codeposition of the copper and lead to create a copper matrix with embedded lead particles. Other materials may be used. For example, U.S. Pat. No. 6,588,934, the disclosure of which is incorporated by reference herein as if set forth at length, discloses a copper-silver combination.
Nevertheless, there remains room for improvement in the art.